GENEVA — Facing what it described as a severe cash shortfall, the United Nations food aid organization said on Monday that it had been forced to suspend a voucher program that was helping to feed 1.7 million Syrian refugees in neighboring countries.

The suspension by the organization, the World Food Program, was one of the most drastic cutbacks ever by an emergency relief provider in the nearly four-year-old Syrian crisis, raising the prospect of widespread hunger at the onset of winter.

The cutback in aid will affect refugees in Egypt, Iraq, Jordan, Lebanon and Turkey who receive voucher cards from the program, which work like debit cards so users can buy food in local shops. The same mechanism also provides an economic lifeline to communities struggling to cope with the influx of Syrian refugees that has swelled since the conflict began in 2011.

“A suspension of W.F.P. food assistance will endanger the health and safety of these refugees and will potentially cause further tensions, instability and insecurity in the neighboring host countries,” Ertharin Cousin, the organization’s executive director, said in a statement from its headquarters in Rome. “The suspension of W.F.P. food assistance will be disastrous for many already suffering families.”

International relief organizations routinely cajole donor countries for more money to deal with the Syria conflict as well as an array of other aid crises, from the Central African Republic to Ukraine, warning of impending disaster if the money does not arrive. Yet it is highly unusual for a major aid provider like the World Food Program to follow through on its admonishments by immediately suspending a major assistance operation.

“We did foreshadow it. We did warn about it,” Emilia Casella, a World Food Program spokeswoman, said in a telephone interview. She denied any suggestion that the suspension was a pressure tactic aimed at donors who have failed to deliver on their pledges. “We’ve exhausted all the options that we had,” she said. “We weren’t crying wolf.”

The United States gave the agency $125 million last week: $70 million to cover the cost of refugee vouchers in November, and $55 million to support food deliveries to about four million people in Syria until year’s end. But the agency said that it needed a further $64 million to support its voucher assistance operation in December and that food aid in Syria would come to a halt in February if it did not receive additional funds.

Once the money arrives, Ms. Casella said, the food voucher cards could be recharged immediately and the suspension would be lifted.

It is not the first time that the World Food Program has reduced assistance because of a budget crisis. Two weeks ago, for example, it curtailed food aid to 500,000 refugees in Kenya displaced by the instability in Somalia and Sudan.

In September, to stretch the funding for its Syria refugee voucher program, it cut up to half the value of the vouchers, which were worth $15 to $45 a month, depending on the country.

To address the growing number of conflicts and disasters, the International Red Cross last week appealed for support for a 2015 budget that is 25 percent greater than this year’s budget. United Nations agencies and their international aid partners will be presenting their appeals for funds to operate in Syria and Iraq to donors this month.

Ms. Casella said that unlike aid providers in housing, health care and education, the World Food Program’s service was essential. “The thing about food is, you can’t not have it,” she said.

The food aid cuts “couldn’t come at a worse time,” António Guterres, the United Nations high commissioner for refugees, said in a statement. “It will impact tens of thousands of the most vulnerable refugee families who are almost entirely dependent on international aid.”

Nick Cumming-Bruce reported from Geneva, and Rick Gladstone from New York.

A version of this article appears in print on , on Page A6 of the New York edition with the headline: U.N. Cuts Food Aid to Refugees From Syria. Order Reprints | Today’s Paper | Subscribe